1. Field of the Invention
The present invention relates to the use of one-dimensional optical data arrays within optical networks.
2. Description of the Related Art
Fiber optics technology has completely penetrated the long-haul telephony network due to its inherent low loss and high bandwidth. In the area of local loop applications, however, financially attractive options have developed more slowly. As of late, substantial research effort has been directed towards developing technology to implement fiber optics within local loop applications (e.g., fiber in the loop). Cost, capacity, and switching problems, however, still must be overcome.
The active double star is an example of fiber optics technology implemented within the local loop. As shown in FIG. 1A, an active double star 10 employs sets of transmitters and receivers T.sub.1, R.sub.1, . . . T.sub.N, R.sub.N, at a central office 20, which transmit and receive downstream and upstream optical signals, respectively, via optical fibers 25.sub.D, 25.sub.U. The central office and fibers act as a primary star. Each optical fiber 25.sub.D, 25.sub.U, is linked to a remote terminal 30, where downstream-directed optical signals are terminated at a receiver R' and then processed (switched) electronically. Downstream optical signals are demultiplexed, re-formed, and launched from transmitters T.sub.1 ' within fibers 35.sub.D to a plurality of optical network units (ONUs) 40 forming a secondary star.
Alternatively, conventional passive optical networks 10' utilize passive optical couplers 32, as shown in FIG. 1B. The passive coupler 32 is located at a remote node 30' to direct downstream optical signals launched from a transmitter 14 at the central office 20. In a passive time division multiplexing or subcarrier multiplexing schemes, optical signals are sent to remote nodes 30' forming the primary star. Each remote node distributes its received optical signal passively, directing similar portions to each of a plurality of optical network units 40 along fibers 35.sub.D to form a secondary star. Filtering means 42 contained at each optical network unit 40 extracts an intended portion of the received signal. During upstream communication, each optical network unit transmits an optical signal within a prearranged time slot or frequency on upstream fiber 35.sub.U. The upstream signals are received at the remote node 30', multiplexed, and directed therefrom to a receiver 16 at the central office 15 via fiber 25.sub.U.
Timing and power budget throughput problems are inherent within PONs operating according to this broadcast distribution. The problems may be avoided, however, utilizing switching methods such as wavelength division multiplexing. A PON network 10" which utilizes wavelength division multiplexing is shown in FIG. 1C. Therein, each transmitter 14' at the central office 20 modulates downstream data at N distinct wavelengths, multiplexing the modulated data signals and transmitting the multiplexed signals onto downstream feeder fibers 25.sub.D. Each feeder fiber 25.sub.D carries the multiplexed signals to an input port P.sub.D of a WDM coupler 32' at remote node 30" for demultiplexing. The demultiplexed signals are passively directed by the WDM coupler to various output ports P.sub.D ' according to wavelength. The output ports direct the signals along downstream fibers 35.sub.D to optical network units 40'. Signals are generated at and transmitted upstream from each optical network unit along fibers 35.sub.U. Said upstream signals are received at ports P.sub.U ', multiplexed within coupler 32', directed to port Pu and fiber 25.sub.U for delivery to the central office. In many PONs, "U" and "D" refer to the same fibers and the same ports.
Remote Interrogation of Terminal Equipment, or RITE-Net.TM., is an emerging passive, WDM-based optical network technology that is disclosed in commonly owned copending U.S. patent application Ser. No. 08/029,724, filed Mar. 1, 1993, and incorporated herein by reference. A RITE-Net.TM. system 10" is shown in FIG. 1D, includes a transmitter 14" and receiver 16" at the central office 20. The transmitter, typically a laser, transmits downstream information, according to wavelength, to a "Dragone" router.sup.1 hereinafter referred to interchangeably as a wavelength division multiplexer/router (WDM/R) 32" or waveguide grating router (WGR) located at remote node 30"'. FNT .sup.1 Dragone et al. Integrated Optics N.times.N Muliplexer On Silicon, IEEE Photon. Technol. Lett., 3, pp. 896-899 (1991); Zirngibl et al., A 12-Frequency WDM Laser Source Based On a Transmissive Waveguide Grating Router, Electronics Letter (1994)
The WDM/R 32" splits optical signals received thereat and directs the split signals to individual optical network units 40" according to wavelength. The optical network units return a portion of the received signal (via upstream fiber 350 after first overmodulating it with optical dam. This avoids the need (and cost) for separate transmitters at each optical network unit and the difficulty of registering and tracking the wavelength of said transmitters. At the remote node 30"', the WDM/R 32" multiplexes the overmodulated upstream signals and directs them via port P.sub.U and fiber 25.sub.U, to the central office.